Mobile ad hoc network is known which is a network formed by only a number of communication terminals performing radio communications, and, in the mobile ad hoc network, autonomous decentralized communication terminals each having similar functions to a router relay communications. When a communication terminal of the mobile ad hoc network (referred to as a “network” below) is to newly participate in the network, the terminal sequentially inquires of the network, for each of all predetermined frequencies assumed to be used by the network, whether the terminal can participate in the network (referred to as a “participation process” below). Through this process, the communication terminal can identify a frequency used by the network to participate in, allowing the terminal to participate in the network. Since a network to participate in generally uses one or a small number of frequencies, communication terminals can participate in the network without taking much time.
Meanwhile, cognitive radio communication is known in which, unused, usable frequency or frequencies are detected from among various frequencies, and communications are performed using any of the detected frequencies. Since unused, usable frequencies change in time, communication terminals for cognitive radio communication perform communications while dynamically changing setting of a frequency to use, radio modulation mode and access method, and the like.
Patent Literature 1 given below discloses a communication terminal for cognitive radio communication. The communication terminal according to Patent Literature 1 includes an interference wave detecting unit and a control unit. The interference wave detecting unit detects, from a received signal including an interference wave, the level and frequency information of the interference wave in a demodulation path. Based on the level and frequency information of the interference wave detected by the interference wave detecting unit, the control unit controls the circuit characteristics of the demodulation path, and based on the level and frequency information of the interference wave detected, also selects a frequency with little influence of the interference wave, as a frequency to use.
With the above-described configurations and operations, the communication terminal according to Patent Literature 1 detects an unused, usable frequency and uses the frequency to enable efficient communication.